Iron arrived late and changed everything. Its ore is common almost everywhere, but working it needs a far hotter and better-controlled fire than copper, and until that was mastered the only iron anyone had was meteoric, metal that had fallen out of the sky. Egyptian has a term for it meaning iron of heaven, and the dagger buried with Tutankhamun is meteoric, confirmed by the nickel content measured in a 2016 analysis. A metal that could not be made and had to be found was worth more than gold, and the reversal once smelting spread was total.
That history left iron with two reputations that contradict each other and both persist. It is the metal of the smith, the weapon and the state, and its Mars attribution is the least strained pairing in the whole scheme. It is also shut out of a striking number of sacred settings. Hebrew scripture forbids iron tools on the stones of the altar. Roman religious practice barred iron from particular rites. Japanese and Korean traditions of ritual construction avoid it in specific places, and in Irish and British fairy belief cold iron repels the otherworld outright.
The usual explanation, that iron was the intrusive new technology arriving on rites already settled in the bronze age, is plausible and is not demonstrable from the sources. What can be said is that one property generates both reputations. Iron is the material that ordinary human labour turns into an edge, and depending on what a rite is for that is either the highest craft or a contamination.
Sources Encyclopedia of ReligionMircea Eliade (ed.); Lindsay Jones (ed., 2nd ed.) with De Re MetallicaGeorgius Agricola, translated by Herbert Clark Hoover and Lou Henry Hoover (1912), An Encyclopedia of Fairies: Hobgoblins, Brownies, Bogies, and Other Supernatural CreaturesKatharine M. Briggs